Year	Number of
1990	16.92
1991	17.24
1992	17.61
1993	18.05
1994	18.51
1995	19
1996	19.68
1997	20.39
1998	21.16
1999	22.02
2000	22.98
2001	24.24
2002	25.64
2003	27.21
2004	28.96
2005	30.9
2006	32.82
2007	34.91
2008	37.28
2009	39.95
2010	43
2011	45.88
2012	49.15
2013	52.77
2014	56.9
2015	61.6
2016	66.91